title: Influence of guest loading on thermal properties of NaxSi136 clathrates.
abstract: Thermal properties of a series of type II clathrates of the formula NaxSi136 with 0 < x < 24 and Na guests occupying the Si cages have been investigated over the temperature range from 2 to 300 K. Heat capacity and thermal conductivity results show that the structure is remarkably responsive to the loading of Na guests. The response is phononic: the host lattice expands in a non-monotonic way, and first stiffens, then relaxes at low loading into the larger Si28 cages (x < 9), then stiffens again as the Na concentration increases further. The response is also electronic, through changes in electronic properties as additional Na is loaded into the smaller Si20 cages at high loading (x > 9). In total, the influence of the guest loading illustrates the complexities of structure-property relations in a guest-host system.
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, NS, B3H 4R2, Canada.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Ritchie
authors.forename: Michel B
authors.initials: MB
authors.lastname: Johnson
authors.forename: John F
authors.initials: JF
authors.lastname: Niven
authors.forename: Matt
authors.initials: M
authors.lastname: Beekman
authors.forename: George S
authors.initials: GS
authors.lastname: Nolas
authors.forename: Jan
authors.initials: J
authors.lastname: Gryko
authors.forename: Mary Anne
authors.initials: MA
authors.lastname: White